___D__ some mammals came to live in the sea is not known.[ ] A.Which B.Since C.Although D.How
问题描述：
___D__ some mammals came to live in the sea is not known.[ ] A.Which B.Since C.Although D.How
为什么不用which 选D 但选how是做known的宾语?
答
how是副词,不能作宾语.这是how引导的主语从句.
how some mammals came to live in the sea 这是主语从句.
哺乳动物如何生活在海洋里.
is not这是系动词
known 这是过去分词做表语.表示被知道.